1. Field of the Invention
This invention relates to crankshaft bearings, and especially to such bearings having flanges designed to accommodate high thrust loads.
2. Description of Prior Developments
It is common practice to support internal combustion engine crankshafts with radial bearings located at spaced points along the crankshaft. For example, for an in-line 4-cylinder or V-8 engine, five equidistantly spaced bearing assemblies are used. Each bearing assembly includes an upper half bearing seated in an arcuate recess in the lower part of the engine cylinder block, and a lower half bearing seated in an arcuate cap structure. The cap structure is bolted to the cylinder block to retain the half bearings encircled around the crankshaft.
At least one of the bearing assemblies is designed to absorb axial thrust forces applied through the crankshaft and received from accessory drive mechanisms such as automatic transmissions. Each half bearing in such a bearing assembly has two axially-spaced flanges designed to seat against side surfaces of the shaft crank arms such that the shaft is prevented from shifting in the axial direction.
In some high performance engines considerable axial thrust is generated in the engine crankshaft during certain operational periods, e.g., during periods of rapid acceleration and deceleration. Very large axial thrust loads may also be developed by the action of the torque converter in the engine transmission. Toroidal motion of the transmission fluid in the torque converter tends to force the impeller and turbine apart, thereby imparting a significant axial thrust force to the crankshaft. The crankshaft thrust bearing is required to absorb such thrust forces.
Axial thrust forces are absorbed by only one or two of the crankshaft half bearings since manufacturing tolerance stack-ups tend to prevent the flanges of multiple bearing assemblies from simultaneous precise pressure contact with multiple axially-spaced surfaces on the crankshaft. When the thrust load is borne by a single flanged bearing assembly, the unit area pressures on the thrust bearing surfaces are relatively high.
Flanged half bearings for rotary crankshafts are shown in U.S. Pat. No. 4,599,147 and U.S. Pat. No. 4,702,624 and U.S. Pat. No. 4,714,356. The half bearings shown therein have radial thrust bearing flanges equipped with oil supply groves or pockets for distributing oil on the flange surfaces, thereby providing at least a partial oil film support between the rotary shaft runner surface and the stationary thrust bearing surface. U.S. Pat. No. 4,488,826 shows the use of wedge film hydrodynamic support applied to a radial bearing construction.
Under high axial thrust load conditions, the oil film support provided by prior art bearings may not always be sufficient to maintain a desired separation between the shaft and the thrust bearing. The oil may be squeezed out of the bearing-shaft interface so as to permit metal-to-metal contact and associated wear of the thrust bearing flange surface.